1. Field of Invention
The invention relates to an optical switch to control the traveling direction of a beam. In particular, the invention relates to an optical switch that uses a magnetic field to lock the switch.
2. Related Art
In general, the optical switch is used to control the traveling direction of a beam. The on-and-off of the switch determines whether a beam is allowed to reach a certain place. Therefore, the optical switch can selectively make a traveling beam reflect from a first traveling direction to a second traveling direction or continue traveling along the first traveling direction. The main method of reflecting a beam using the optical switch is to employ a reflective mirror to reflect the light. In recent years, the optical switch is evolved from normal sizes down to one that utilizes the micro-electro-mechanical system (MEMS) manufacturing technology, achieving the goal of minimizing optical switches. Another important direction is to make a large matrix of optical switches.
An optical switch matrix comprised of four optical switches is shown in FIG. 1. Light beams L1, L2 propagate in a first traveling direction along fiber optic cables 1a, 1b. After leaving the fiber optic cables 1a, 1b, they still travel in the same direction until they hit a mirror 4 and get reflected into a second traveling direction. Afterwards, the beams follow the fiber optic cables 2a, 2b to continue their courses. Of course, when the light beams L1, L2 are not reflected by the mirror 4 to the second traveling direction, they can keep going in the first traveling direction and propagate to fiber optic cables 3a, 3b. 
The mechanism that switches the mirror 4 between the reflective position and the non-reflective position can use electrostatic force to generate a minute torque on the mirror, see JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 17, NO. 1, JANUARY 1999 (xe2x80x9cFree-Space Fiber-Optic Switches Based on MEMS Vertical Torsion Mirrorsxe2x80x9d). However, this switching method requires continuous power consumption to keep the mirror at the reflective position. Furthermore, since a torsion generated by the electrostatic force is used to switch the rotator between the reflective position and the non-reflective position, the lifetime of the device may not be predictable due to unexpected machine fatigue.
Another method that uses a magnetic force as the driving force is proposed in IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 5, NO. 1, JANUARY/FEBRUARY 1999 (xe2x80x9cElectromagnetic Torsion Mirrors for Self-Aligned Fiber Optic Crossconnectors by Silicon Micromachiningxe2x80x9d). This device mainly includes a magnet, a coil, a substrate, and a mirror. The magnet is installed on the substrate under the rotatable mirror. It has the function of locking the mirror at a specific position. As the mirror is coated with a magnetic material, the mirror will rotate by 90 degrees to a perpendicular position once the coil is imposed with a current. Therefore, this device can be used as an optical switch. Nevertheless, this method has the following drawbacks:
1. A larger magnetic field is needed in order to rotate the mirror by 90 degrees.
2. The mirror is susceptible to external disturbance and vibrates or even deviates from its locking position, resulting in noisy light signals.
3. Since the mirror rotates 90 degrees, the torsional bar has to be elongated to avoid limit stress tension, thus increasing the total area.
In view of the foregoing, it is highly preferable to provide an optical switch with a stable locking function and satisfying the need for a large optical matrix. It is further desirable to minimize the optical switch to save energy.
An objective of the invention is to provide an optical switch which has a reflective position and a non-reflective position for the optical switch by establishing a stable magnetic field having a potential with two minima. When the provided driving force conquers the potential and drives the optical switch to the other potential minimum, the optical switch is automatically locked at the other position even after the driving force is removed. This invention can achieve the goals of increasing lifetime, enhancing dynamical properties, and stabilizing the locking while minimizing power consumption.
In accordance with the disclosed optical switch, a beam can be selectively reflected or allowed to pass. It has a substrate, two magnetic objects, a rotator, and a driving device. The two magnetic objects are installed on both surfaces of the substrate for providing a magnetic field. The driving device is pivotally installed between the two magnetic objects on the substrate and has a mirror and a magnetic material. Under the magnetic field of the magnetic objects, the rotator can be selectively and firmly locked at a reflective position to reflect beams and a non-reflective position for the beam to pass. The driving device is installed close to one surface of the substrate corresponding to the rotator to provide a driving force to switch the rotator between the reflective position and the non-reflective position.
Therefore, when the rotator is at the reflective position, the mirror on the rotator can reflect the beam. If the driving device now provides a driving force to rotate the rotator to the non-reflective position, the beam is then allowed to keep traveling without reflection. On the contrary, if the driving device provides a driving force to rotate the rotator from the non-reflective position to the reflection position, the beam is then reflected to travel in another direction.